ALT_06C0: Quasi-continuous, surface measurements from Alert, Nunavut, Canada located at 82.4508N, 62.5056W and 200.00 masl. Measurements are made by Environment Canada (EC). Assimilation statistics for this and other sites are included in the Documentation.

Time series of CO2 mole fractions, both
simulated and observed, at this CarbonTracker observation site. In
the top panel, measured mole fractions (open black
circles) are plotted along with CarbonTracker simulated values (light blue open circles). At
some sites, there are observations that CarbonTracker can not
simulate successfully; these are shown as filled red circles. The observations
corresponding to these rejected simulated values are shown with
open red circles. The bottom panel
shows a time series of residuals--the difference between the
simulated and measured mole fractions--shown with dark green open circles. These
residuals should be uncorrelated in time, unbiased (i.e., have a mean
of zero), and distributed normally. Also shown in the lower panel is
the imposed model-data mismatch (orange lines), which in part defines
the rejection criterion (see documentation). Any
model first guess value which is more than three times the MDM away
from zero, after accounting for potential adjustments to the
simulated value due to optimizing fluxes, is rejected by the
optimization system. Rejected values, if there are any, are shown
with filled red circles.

Seasonal histograms of the residuals at this site. See caption for
top figure for the definition of residuals. The left panel collects
all residuals for each northern hemisphere summer (June through
September); the right panel is the northern hemisphere winter
(November through April). Residuals before 1 Jan 2001 are excluded
from this analysis to avoid an effect of CarbonTracker burn-in from a
poorly-known initial CO2 distribution.
The tan color shows
the histogram of the residuals themselves; the blue lines and
statistics shown in blue text are a summary of the residuals
interpreted as a normal distribution. The assumed model-data mismatch
is shown in green (lines and text). The vertical scales are relative,
determined by the number of observations and how tightly they are
grouped, with the area under the histogram forced to unity.